On Mon, Aug 10, 2026 at 6:23 AM <[email protected]> wrote:
>
> From: Kyrylo Tkachov <[email protected]>
>
> The conditional-compare expander accepts a plain boolean as a comparison
> against zero. This is useful when a chain also contains an explicit
> comparison. It is harmful when every leaf is a boolean. For example:
>
> _Bool
> f (_Bool x, _Bool y)
> {
> return x || y;
> }
>
> AArch64 emitted:
>
> and w1, w1, 255
> tst w0, 255
> ccmp w1, 0, 0, eq
> cset w0, ne
>
> After this patch it emits one bitwise operation:
>
> orr w0, w0, w1
>
> Require at least one explicit comparison in a conditional-compare tree.
> Mixed boolean and comparison chains remain accepted.
>
> Bootstrapped and tested on aarch64-none-linux-gnu.
> Ok for trunk?
> Thanks,
> Kyrill
>
> gcc/
>
> PR middle-end/109832
> * ccmp.cc (ccmp_tree_has_comparison_p): New function.
> (expand_ccmp_expr): Reject an all-boolean tree.
>
> gcc/testsuite/
>
> PR middle-end/109832
> * gcc.target/aarch64/ccmp_7.c: New test.
>
> Signed-off-by: Kyrylo Tkachov <[email protected]>
> ---
> gcc/ccmp.cc | 24 ++++++++++++
> gcc/testsuite/gcc.target/aarch64/ccmp_7.c | 46 +++++++++++++++++++++++
> 2 files changed, 70 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/aarch64/ccmp_7.c
>
> diff --git a/gcc/ccmp.cc b/gcc/ccmp.cc
> index 1c540f641b2..9f7670bf58e 100644
> --- a/gcc/ccmp.cc
> +++ b/gcc/ccmp.cc
> @@ -93,6 +93,25 @@ ccmp_tree_comparison_p (tree t, basic_block bb)
>
> typedef hash_map<tree, bool> ccmp_uniform_cache;
>
> +/* Return true if AND/IOR tree T contains a comparison in BB. */
> +
> +static bool
> +ccmp_tree_has_comparison_p (tree t, basic_block bb)
> +{
> + gimple *g = get_gimple_for_ssa_name (t);
> + if (!g || !is_gimple_assign (g))
> + return false;
> +
> + tree_code code = gimple_assign_rhs_code (g);
> + if (TREE_CODE_CLASS (code) == tcc_comparison)
> + return gimple_bb (g) == bb;
> + if (code != BIT_AND_EXPR && code != BIT_IOR_EXPR)
> + return false;
> +
> + return (ccmp_tree_has_comparison_p (gimple_assign_rhs1 (g), bb)
> + || ccmp_tree_has_comparison_p (gimple_assign_rhs2 (g), bb));
Is there a way to do this non recursive (and not with a work list)?
I think it might be a good idea to move ccmp away from expand into say isel.
We already don't really want to depend on TER and your above code does
not even use ter.
> +}
> +
> /* Return true if T is a CODE tree in BB whose leaves are comparisons.
> CACHE records results for logical SSA definitions. */
>
> @@ -368,6 +387,11 @@ expand_ccmp_expr (gimple *g, machine_mode mode)
> if (!ccmp_candidate_p (g, cache, true))
> return NULL_RTX;
>
> + basic_block bb = gimple_bb (g);
> + if (!ccmp_tree_has_comparison_p (gimple_assign_rhs1 (g), bb)
> + && !ccmp_tree_has_comparison_p (gimple_assign_rhs2 (g), bb))
> + return NULL_RTX;
> +
> last = get_last_insn ();
>
> rtx_insn *prep_seq = NULL, *gen_seq = NULL;
> diff --git a/gcc/testsuite/gcc.target/aarch64/ccmp_7.c
> b/gcc/testsuite/gcc.target/aarch64/ccmp_7.c
> new file mode 100644
> index 00000000000..29e269b854e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/ccmp_7.c
> @@ -0,0 +1,46 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +/* PR middle-end/109832 */
> +
> +/* A conditional compare folds a comparison into the flags. When the
> operands
> + are plain booleans there is no comparison to fold and the bitwise
> operation
> + is cheaper, so no conditional compare should be formed. */
> +
> +_Bool
> +bool_ior (_Bool x, _Bool y)
> +{
> + return x || y;
> +}
> +
> +_Bool
> +bool_and (_Bool x, _Bool y)
> +{
> + return x && y;
> +}
> +
> +extern _Bool t (void);
> +
> +_Bool
> +bool_call_ior (void)
> +{
> + _Bool x = t ();
> + _Bool y = t ();
> + return x | y;
> +}
> +
> +_Bool
> +bool_ior_tree (_Bool a, _Bool b, _Bool c, _Bool d)
> +{
> + return (a | b) | (c | d);
> +}
> +
> +/* One explicit comparison is enough to keep each chain profitable. */
> +
> +int
> +bool_and_cmp_tree (_Bool a, _Bool b, _Bool c, int x, int y)
> +{
> + return ((a & b) & c) & (x < y);
> +}
> +
> +/* { dg-final { scan-assembler-times {\tccmp\t} 3 } } */
> +/* { dg-final { scan-assembler-times {\torr\t} 5 } } */
> --
> 2.50.1 (Apple Git-155)
>
